1,721,019 research outputs found
OBSERVATION OF FRESNEL DIFFRACTION IN A 2-BEAM LASER INTERFEROMETER
No full textA displacement-angle interferometer capable of 10(-6) resolution in fringe division was developed for the precise measurement of the silicon (220) lattice spacing by x-ray and optical interferometry. With a view to achieving 10(-8) measurement uncertainty, the interference pattern was studied by the Fresnel (Gaussian) scalar approximation of the free-space propagation of interfering beams. Imperfect alignment and diffraction phenomena having been identified, and subsequently experimentally proved, as important error sources, remedial steps were identified and taken with consequent improvement of the experiment accuracy. The investigation brought into light theoretical and experimental evidences of corrections to the interference phase which were overlooked in previous analyses
PHASE HOLONOMY IN OPTICAL INTERFEROMETRY
No full textThe delivering of two-frequency beams by optical fibres and interferometers and the interference of polarized waves is studied by using Jones' formalism and the complex-wave representation. Polarization encoding is shown to make the relation between the phase of the interference pattern and the difference in the optical path of interfering beams nonlinear, owing to the geometric contribution to the phase made by misalignments and unequal ellipticity of the normal modes of beam and interferometer. The polarization transport is analysed with the aid of the Poincare representation, and a complete picture of the phenomena underlying nonlinearity and geometric noise is given. In the case of small aberrations approximate formulae and experimental observations are reported as well
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A two-axis tip-tilt platform for x-ray interferometry
No full textWe describe the design and demonstrate a two-axis tip-tilt platform stacked on a translation stage for combined x-ray and optical interferometry. The platform is electronically controlled to compensate for parasitic rotations and straightness errors. The key characteristic of the platform is the way in which it carries out translations and rotations by sliding. In spite of the potential stop-and-go motion, an x-ray interferometer was successfully operated and guiding errors were kept to within 1 nrad and 1 nm. The platform made it possible to move the x-ray interferometer by up to a couple of millimetres. In addition, the combined x-ray and optical interferometer allowed us to investigate the microdynamics of sliding
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Optically polished surfaces parallel to the (220) lattice planes of silicon monocrystals
No full textAn apparatus whereby silicon monocrystals, such as those used in x-ray optics, can be cut and optically polished accurately parallel to known lattice planes is described. A parallelism to within 10 mu rad has been obtained
Scanning X-ray interferometry over a millimeter baseline
No full textA new translation device has been developed at the Istituto di Metrologia ''G. Colonnetti'' (IMGC) to improve the measurement of the (220) lattice spacing in silicon by X-ray/optical interferometry, It is capable of millimeter linear displacement and servo controls ensure picometer and nanoradian resolutions in crystal position and attitude, It has been successfully used to drive a scanning X-ray interferometer over a 2 mm displacement, thus extending by more than one order of magnitude the maximum crystal movement obtained before
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